TRPV1 - Hacking

Hacking

One example of modularity and hacking opportunity is the heat activation domain. TRPV proteins are activated by heat on the C-termimus, while TRPM proteins are activated by cold temperatures (<23-28°C) in the same location. Exchanging the C-terminals for each other, could then activate these proteins at different than normal temperatures. Chemical genetics has also been used to introduce TRPV1 into cells that do not normally express it. When capsaicin is added, those cells are then activated by the influx of calcium. This system is not as fast as other controls, such as optogenetics, but remains an important mechanism of spatial and temporal control. This method of control can be applied to a variety of systems and cells, and will most likely be expanded and improved in the near future.

The aforementioned capsaicin-activated TRPV1 model allows for transient, reversible, and sensitive control of neurons. Even before the TRPV1 ion channel was identified, capsaicin has been used to conditionally activate nociceptors to study brain circuitry. Recently, embryonic stem cell technology and chemical genetics have allowed for the production of mice genetically engineered to express TRPV1 upon Cre recombinase-mediated recombination in non-nociceptive neurons. Upon treatment with a lentiviral vector engineered to express Cre, TRPV1 is expressed and consequently, treatment with capsaicin results in the production of inward currents in the targeted neurons. No capsaicin-induced currents are observed in TRPV1-expressing non-virally treated mice.

Breeding the TRPV1-expressing mice with mice expressing a transgenic nestin-Cre promoter yields a population of offspring that express both TRPV1 and Cre. Upon infusion with capsaicin, these mice exhibit capsaicin-induced action potential firings. Expectedly, the offspring that only express TRPV1 show no response to capsaicin. It was further shown that this model can be reproduced in other types of neurons, generating similar results. Also, it can be used in vitro or in vivo to show the effects of capsaicin treatment in awake TRPV1-Cre-expressing mice. This technology provides another system in which mammalian circuitry may be studied, especially because it may be used to activate structures inaccessible to light, which are impossible to examine using optogenetic techniques.